The present invention relates to multiple imaging, and more particularly to an improved method for producing multiple-image media and to media produced by such method.
The production of images which change with a change in viewing angle has been known for many years. Such technology is described, for example, in G. Anderson, U.S. Pat. No. 2,815,310. The images are produced on opaque or transparent sheets of material such as paper, paperboard or plastic. The resulting imprint, in black and white or color, is laminated to a transparent lenticular lense. Alternatively, a transparent plastic carrier may be printed on the reverse side and viewed through a lenticular lense face of the carrier.
A lenticular screen, as is well known, has a number of lenses arranged in a side-by-side relationship on one face. Each lense, commonly termed a lenticle, may be formed by an elongated or circular convex frontal surface, and a flat rear surface.
The printed image is formed by two interleave pictures producing a grid or parallel lines with alternating striations. The pitch, or number of picture element pairs per unit distance, is the same as the lense pitch of the lenticular array. The focal lense of each of the lenticles should be equal to the thickness of the lenticular sheet. Under these conditions, at one viewing angle an observer will see only one picture, while at a different angle the same observer will see the other picture.
The requirement that the picture elements be in registration with the lenticular array complicates the printing and lense forming steps. In practice, the pitch of the lenticular assembly is limited to a spacing that is equivalent to 100 lenticles per inch, or less. Even with 50-100 lenticles per inch, it is difficult to hold the registration over widths of more than a few inches. This limitation restricts the image resolution, as well as size.
U.S. Pat. No. 3,284,208 to Land discloses a photomechanical printing method and apparatus for forming color screen elements using lenticular media. In the Land method, at a first stage a "photo-responsive layer" such as potassium, sodium or ammonium dichromate sensitized gelatin, is laid down on the flat side of the lenticular sheet. The gelatin is then irradiated with radiation (such as ultraviolent radiation) which is actinic to the photo-responsive layer. The element is contacted with water or other suitable solvent to remove unexposed portions of the photo-responsive layer, and the element then contacted with a dye solution substantive to the remaining portions of the photo-responsive layer to provide optical filter elements. The layer is then coated with an adhesive layer for protection; after such layer dries, the process may be repeated.
U.S. Pat. No. 3,617,281 to Lindin discloses a system for printing lenticular films using collimated light, according to the Land process.
Commonly assigned copending U.S. Pat. Application No. Ser. No. 225,505 discloses a method for imprinting of lenticular films, and improved films made by such method. The flat face of a lenticular film disclosed therein (having an array of lenticles on the opposite face) is imprinted with a visible light absorbing ultraviolet radiation sensitive imaging layer which is irradiated with collimated light through the lenticular sheet to render portions of the layer insoluble to a predetermined solvent. The layer is then washed with such solvent to remove the still-soluble solvent thereof. This method has two major advantages over that of the Land and Lindin patents, i.e., it eliminates the need to subsequently imbibe a photo-responsive layer with a separate dye or other color material, since the imaging layer itself contains the visible light absorping materials. This permits, e.g., the imprinting of an arbitrary multi-color pattern and the subsequent selective removal of the pattern. Furthermore, applicant's prior art method eliminates the need for the adhesive (protective) layer. These two process differences result in a simpler, less expensive, and more rapid process.